7 .. image:: /images/picN.png
14 obody understands the phrase *errare humanum est* quite in the same way
15 as a programmer does. Computers are highly efficient machines capable of
16 wondrous calculations, but they lack imagination and insist that every
17 single item thrown at them must be presented according to certain rules
18 previously defined. You can't negotiate with a computer; you either bow
19 in submission or bite the dust.
21 Inform behaves no differently. If you make a typing or syntax mistake,
22 the compiler will send you back to revise your work. "It was just a
23 lousy comma!" you cry in disgust. The compiler remains silent. It has
24 nothing to gain by argument, because it’s always right. So you go and
25 change the lousy comma. No harm done except perhaps to your pride.
27 Errors that are found during compilation may be tedious to correct, but
28 are usually easy to find; after all, the compiler tries politely to
29 point out what and where the mistake was. Trouble begins after you've
30 managed to satisfy all of the compiler's complaints. You are rewarded by
31 a clean screen, devoid of a list of errors, and you are offered -- a
34 A new file has appeared in your folder. A story file. Yes, *the* game.
35 You quickly open your favourite interpreter and begin to play -- only to
36 discover the dark side of errors, the bugs. Bugs come in all shapes,
37 colours and sizes: big, small, stupid, absurd, minor, disturbing,
38 nerve-wracking and catastrophic. They are often unpredictable: they
39 regale our eyes with surprising, unexpected behaviour. They defy logic:
40 I can TAKE the key, and the game even says "Taken", but the key remains
41 in the same place and won't appear in my inventory. Or: opening the door
42 while wearing the fur coat causes a programming error and a cryptic
43 message "tried to find the attribute of nothing". And many, many others.
45 When designing a game you try to take into consideration the states that
46 your objects will find themselves in, but any medium-sized game has such
47 a number of objects and actions that it's almost impossible to think of
48 all the possible variations, permutations and possibilities.
50 Debugging consists in finding run-time errors, and then correcting them.
51 Pretty easy, you might think, but no. Detection of such errors is not
52 straightforward, since they tend to manifest themselves only under
53 precise circumstances. Then you have to investigate your code to find
54 out what is causing them. And then, if you discover the offending lines,
55 you must make the appropriate changes. (There is also the case when you
56 can't find the mistake. Don't worry, it's there somewhere. Persistence
57 always pays off in the end.)
59 To help you out in this daunting task, Inform has a stock of special
60 actions: the debugging verbs. They become available at run-time when the
61 source file is compiled in **Debug mode** (``-D switch``). When you are
62 ready to release your game, you’ll have to recompile, switching off
63 Debug to avoid allowing the players to benefit from the debugging verbs.
64 We'll cover briefly a few of these actions, and tell you what they do.
70 The only way to test a game is to play it. As you make progress writing
71 code, the game grows complicated, and it becomes really tiresome to
72 repeat all the commands every time you play. Not unusually, when you fix
73 the behaviour of some object, you are also affecting the behaviour of
74 other objects or actions, so it's a good idea to test everything now and
75 then; you have to make sure that your recent changes and fixes didn't
76 spoil something that previously worked fine.
78 The RECORDING command (RECORDING ON and RECORDING OFF) saves the
79 commands that you type as you play into a text file (you'll probably be
80 prompted for a file name). When you add a new section to the game, you
81 can play to that point, type RECORDING ON to capture (in another file)
82 the commands which exercise that section, and then later use your editor
83 to append those new commands to the existing list.
85 The REPLAY command runs the text file created by RECORDING, playing all
86 the stored commands in one go. This way you can very quickly check
87 whether everything is working as it should.
89 You can open the file of commands with any text editor program and
90 modify the contents as need arises: for instance, if you want to delete
91 some commands no longer necessary because of a change to the game, or if
92 you forgot to test some particular object and you need to add new
95 This technique (the use of recorded lists of commands) is, and we can't
96 emphasise it too strongly, one of the most useful testing features for a
103 Some debugging verbs offer information about the current state of things.
107 This action lists all the objects in the game and how they contain
108 each other. You can discover the possessions of just one object by
109 typing TREE *object*. All the objects that you have defined in the
110 source file are turned into numbers by Inform when it compiles the
111 story file; this command also lists those internal
112 :samp:`{obj_id}` numbers.
116 Displays information about the *object*, the attributes it currently
117 has and the value of its properties. The *object* can be anywhere,
118 not necessarily in scope. For instance, in "Heidi":
120 .. code-block:: transcript
123 Object "bird's nest" (29) in "yourself"
124 has container moved open workflag
125 with name 'bird's' 'nest' 'twigs' 'moss',
126 description "The nest is carefully woven of twigs and moss." (19230),
130 Displays the grammar of the *verb*, just like a standard ``Verb``
131 definition. This comes in handy when you have tampered with ``Extend``
132 and are not sure about the final results of your machinations. An
133 example from "William Tell":
135 .. code-block:: transcript
138 Verb 'feed' 'give' 'offer' 'pay'
139 * held 'to' creature -> Give
140 * creature held -> Give reverse
141 * 'over' held 'to' creature -> Give
142 * 'homage' 'to' noun -> Salute
144 The first lines reproduce the verb definition as it's written in the
145 library. The last line, however, is the direct consequence of our
148 .. code-block:: inform6
151 * 'homage' 'to' noun -> Salute;
155 Lists all of the objects currently in scope (in general terms, visible
156 to the player character). More powerfully, you can type SCOPE *object*
157 to discover which objects are in scope for the named *object*. This
158 feature becomes useful when you have NPCs capable of tampering with
162 What on earth is going on?
163 ==========================
165 There comes the time when some actions don't produce the desired effects
166 and you don't know why. The following debugging verbs offer information
167 about what the interpreter is up to, which might enable you to identify
168 the moment when things started to go awry.
170 ACTIONS (or ACTIONS ON ) and ACTIONS OFF
172 Gives information about all the actions going on. Some actions get
173 redirected to others, and this becomes at times a source of mischief
174 and mystery; here you get a clue what's happening. For example, take
175 this transcript from "William Tell":
177 .. code-block:: transcript
179 Further along the street
180 People are still pushing and shoving their way from the southern gate towards
181 the town square, just a little further north. You recognise the owner of a fruit
184 Helga pauses from sorting potatoes to give you a cheery wave.
187 [ Action Search with noun 35 (fruit and vegetable stall) ]
188 [ Action Examine with noun 35 (fruit and vegetable stall) (from < > statement) ]
189 It's really only a small table, with a big heap of potatoes, some carrots and
190 turnips, and a few apples.
193 CHANGES (or CHANGES ON ) and CHANGES OFF
195 Tracks object movements, and changes to properties and attributes:
197 .. code-block:: transcript
200 There is less of a crush in the middle of the square; most people prefer to
201 keep as far away as possible from the pole which towers here, topped with that
202 absurd ceremonial hat. A group of soldiers stands nearby, watching everyone who
206 [Setting Middle of the square.warnings_count to 1]
207 A soldier bars your way.
209 "Oi, you, lofty; forgot yer manners, didn't you? How's about a nice salute for
213 [Setting Middle of the square.warnings_count to 2]
215 "I know you, Tell, yer a troublemaker, ain't you? Well, we don't want no bovver
216 here, so just be a good boy and salute the friggin' hat. Do it now: I ain't
217 gonna ask you again..."
220 [Setting hat on a pole.has_been_saluted to 1]
221 You salute the hat on the pole.
223 "Why, thank you, sir," sneers the soldier.
226 [Setting Middle of the square.warnings_count to 0]
227 [Setting hat on a pole.has_been_saluted to 0]
228 [Moving yourself to South side of the square]
231 TIMERS (or TIMERS ON ) and TIMERS OFF
233 This verb shows you the state of all active timers and daemons at the
234 end of each turn. We haven't mentioned timers -- similar to daemons --
235 in this guide; you might perhaps use one to explode a bomb ten turns
236 after lighting its fuse.
238 TRACE (or TRACE ON ), TRACE *number* and TRACE OFF
240 If you turn on this powerful verb, you'll be able to follow the
241 activity of the **parser** -- that part of the library which tries to
242 make sense of what the player types -- and this will indeed be a
243 wonderful moment of gratitude that someone else took the trouble of
244 writing it. Since the parser does so many things, you can decide the
245 level of detail about the displayed information with the *number*
246 parameter, which can go from 1 (minimum info) to 5 (maximum info). By
247 default, TRACE ON and TRACE with no number sets level 1. Trace level
248 1 shows the grammar line that the parser is thinking about, while
249 level 2 shows each individual token on each grammar line that it
250 tries. The information displayed with higher levels may become quite
251 hacky, and you are advised to use this feature only if nothing else
260 This action lets you teleport to the room where the *object* is. This
261 is useful when, for example, certain parts of the map are closed
262 until the player character solves some puzzle, or if the game map is
263 divided in different areas. If the room you want to visit has no
264 objects, you can use...
268 Teleports you to the room with that internal *number*. Since rooms
269 usually have no name, you'll have to discover the internal number of
270 the room object (with the command TREE, for instance).
274 PURLOIN works exactly as TAKE , with the nice addition that it doesn't
275 matter where the object is: in another room, inside a locked
276 container, in the claws of the bloodthirsty dragon. More dangerously,
277 it doesn't matter if the object is takeable, so you may purloin
278 ``static`` or ``scenery`` objects. PURLOIN is useful in a variety of
279 situations, basically when you want to test a particular feature of
280 the game that requires the player character to have some objects
281 handy. Instead of tediously collecting them, you may simply PURLOIN
282 them. Be careful: it's unwise to PURLOIN objects not meant to be
283 taken, as the game's behaviour may become unpredictable.
285 ABSTRACT *object* TO *object*
287 This verb enables you to move the first *object* to the second
288 *object*. As with PURLOIN , both objects can be anywhere in the game.
289 Bear in mind that the second object should logically be a
290 ``container``, a ``supporter`` , or something ``animate``.
293 Infix: the harlot's perogative
294 ==============================
296 The basic debugging verbs are fairly versatile, easy to use, and don't
297 consume a lot of memory. Occasionally though, you'll meet a bug which
298 you simply can't catch using regular techniques, and that’s when you
299 might want to investigate the Infix debugger. You'll need to compile
300 using the ``-X`` switch, and you'll then be able to monitor and modify
301 almost all of your game’s data and objects. For instance, you can use
302 ";" to inspect -- and change -- a variable:
304 .. code-block:: transcript
307 Benny's offers the FINEST selection of pastries and sandwiches. Customers clog
308 the counter, where Benny himself manages to serve, cook and charge without
309 missing a step. At the north side of the cafe you can see a red door connecting
318 *** You have been SHAMEFULLY defeated ***
320 In that game you scored 0 out of a possible 2, in 2 turns.
322 It's often quite maddening to realise that some variable is still
323 ``false`` because the Chalk puzzle didn't work properly, and that you
324 can't test the Cheese puzzle until the variable becomes ``true``. Rather
325 than quit, fix the Chalk, recompile, play back to the current position
326 and only *then* tackle the Cheese, how much easier to just change the
327 variable in mid-stream, and carry right on.
329 You can use ``;WATCH`` to monitor an object; you'll see it receive
330 messages and you'll be told when its property and attribute values
333 .. code-block:: transcript
336 ; Watching object "Middle of the square" (43).
339 [Moving yourself to Middle of the square]
340 [Moving local people to Middle of the square]
341 [Moving Gessler's soldiers to Middle of the square]
342 [Moving your son to Middle of the square]
345 There is less of a crush in the middle of the square; most people prefer to
346 keep as far away as possible from the pole which towers here, topped with that
347 absurd ceremonial hat. A group of soldiers stands nearby, watching everyone who
349 [Giving Middle of the square visited]
352 [ "Middle of the square".before() ]
353 [ mid_square.before() ]
354 [Setting Middle of the square.warnings_count to 1]
355 A soldier bars your way.
357 "Oi, you, lofty; forgot yer manners, didn't you? How's about a nice salute for
361 [ "Middle of the square".before() ]
362 [ mid_square.before() ]
363 [Setting Middle of the square.warnings_count to 2]
365 "I know you, Tell, yer a troublemaker, ain't you? Well, we don't want no bovver
366 here, so just be a good boy and salute the friggin' hat. Do it now: I ain't
367 gonna ask you again..."
370 [ "Middle of the square".before() ]
371 [ mid_square.before() ]
372 [Setting Middle of the square.warnings_count to 3]
374 "OK, Herr Tell, now you're in real trouble.
377 .. todo:: "Herr" above is italicized. Was that a mistake in the original text?
379 Infix is quite complex -- there are more commands than those we have
380 shown you -- so while it's good to have available, it's not really a
381 tool for novices. If you do use it, be careful: you get a lot of runtime
382 power, and may easily screw up the state of the game. Remember, however,
383 that the changes affect only the current story file while it’s running;
384 to make permanent amendments, you still need to edit the source file.
386 You won't need it often, but Infix can sometimes provide quick answers
393 Your game will still have some undetected bugs despite all your efforts
394 to clean it up. This is normal, even for experienced designers; don't
395 feel discouraged or demoralised. You might find it reassuring to know
396 that our own example games in this guide -- which certainly don't
397 qualify as "complex programming" -- were far from perfect at the First
398 Edition. We blush at the following report from an extremely diligent
401 I found these things when playing “Captain Fate”:
403 * player is able to wear clothes over the costume,
405 * player can change into costume in the dark unlocked bathroom without
408 * player can drop clothes in the dark unlocked bathroom. Try REMOVE
409 CLOTHES. X SELF. REMOVE COSTUME. INV -- X SELF says that you
410 are wearing the costume, but the inventory does not reflect this.
412 The Second Edition fixed those problems, and quite a few more besides.
413 "That's it;" we thought, "after all this time, our example games are
414 sure to be squeaky clean." In our dreams... Another diligent play-tester
417 While reading I took notes of some mistakes and inconsistencies:
419 * BENNY, GIVE KEY TO CUSTOMERS and BENNY, GIVE KEY will
420 make Benny give the key to the player. The same goes for coffee.
422 * Benny will force the player back into the cafe even when the key is
423 dropped in the café, or put on the counter (in Benny's plain sight!).
425 Of course, the code we've offered you in this edition takes care of
426 those embarrassing issues, but it might very well happen that a few more
427 undetected absurdities pop up from now on.
429 The final stage of debugging must happen elsewhere, at the hands of some
430 wilful, headstrong and determined beta-testers; these are the people
431 who, if you’re lucky, will methodically tear your game to shreds and
432 make extensive reports of things that don't work reliably, things that
433 don't work as smoothly as they might, things that ought to work but
434 don't, things that never even crossed your mind (like, uh, dropping the
435 costume in the dark). Once you think your game is finished -- in that it
436 does all that you think it should, and you've run out of ideas on how
437 else to test it -- look for a few beta-testers; three or four is good.
438 The IF community offers some beta-testing resources, or you can always
439 ask in RAIF for kind souls willing to have a go at your game. Remember
442 * **Expect no mercy**. Although it hurts, a merciless approach is what
443 you need at this time; much better to discover your errors and
444 oversights now, before you release the game more widely. And don't
445 forget to acknowledge your testers' assistance somewhere within the
448 * **Never say never**. If your testers suggest that the game should
449 respond better to an attempted action, don't automatically respond
450 with "No one's going to try that!" They already have, and will again
451 -- be grateful for your testers' devious minds and twisted psyches.
452 Although a normal player won't try all of those oddball things,
453 every player is bound to try at least one, and their enjoyment will
454 be greater, the reality enhanced, if the game "understands".
456 * **Ask for more**. Don't treat your testers simply as validators of
457 your programming skills, but rather as reviewers of your
458 storytelling abilities. Encourage them to comment on how well the
459 pieces fit together, and to make suggestions -- small or radical --
460 for improvement; don't necessarily reject good ideas just because
461 implementing them "will take too long". For example: "the scene in
462 the Tower of London doesn't somehow seem to belong in an Arabian
463 Nights game", or "having to solve three puzzles in a row just to
464 discover the plate of sheep's eyes is a little over the top", or
465 "this five-room trek across the desert really is a bit dull;
466 perhaps you could add a quicksand or something to liven it up?", or
467 "the character of the eunuch in the harem seems to be lacking in
468 something". That is, view the testers collectively not as simple
469 spell-checkers, but rather as collaborative editors on your latest
projects / ibg.git / blob